One of the most important ways to keep your body healthy is by exercising — it has been shown to help prevent chronic disease, lengthen life, ward off dementia, slow cognitive decline and much more.However, the amount of sleep you get may be just as important — at least when it comes to the benefits of exercise and how well your brain functions as you age.Video above: Short naps may be the key to reducing the risk of dementia In a new study, researchers discovered people with more frequent, higher-intensity physical activity who slept less than six hours a night on average had faster overall cognitive decline than short sleepers who exercised infrequently.“Our study suggests that getting sufficient sleep may be required for us to get the full cognitive benefits of physical activity,” said lead author Dr. Mikaela Bloomberg, a research fellow at the Institute of Epidemiology & Health Care at University College London.“It shows how important it is to consider sleep and physical activity together when thinking about cognitive health,” she said in a statement.Decade-long studyResearchers followed nearly 9,000 adults for over 10 years who were part of the English Longitudinal Study of Ageing, a longitudinal study on people older than age 50 funded by the U.K. government and the U.S. National Institute on Aging. In addition to an initial workup, participants go through a follow-up interview and cognitive testing every two years.Anyone with a dementia diagnosis or with test scores that suggested cognitive decline were excluded from the study, which published Wednesday in The Lancet Healthy Longevity journal.Building upon evidence from prior research, the new study found people who had higher levels of physical activity and also slept between six and eight hours per night had better cognitive function as they aged.Concurrently, being less physically active and sleeping poorly were independently associated with worse cognitive performance over time. In addition, sleeping less than six hours a night was linked with faster rate of cognitive decline over time.The most physically active group in the study were younger and thinner at baseline, married or partnered, less likely to smoke, drink or have chronic depression or illness and had higher levels of education and wealth than the least active group.Despite those advantages, at the end of 10 years, highly active people in their 50s and 60s who slept on average less than six hours a night lost the advantage that exercise provided — they declined more rapidly and had the same cognitive levels as people who didn’t exercise.“We were surprised that regular physical activity may not always be sufficient to counter the long-term effects of lack of sleep on cognitive health,” Bloomberg said.In addition, physically active short sleepers in their 50s and 60s experienced more rapid cognitive decline compared with better sleepers — but only to a certain age. In people age 70 and older, the benefits of exercise on the brain was maintained, despite short sleep.“By age 70 years, the cognitive benefit associated with higher physical activity was maintained over the ­10-year follow-up period,” the authors said, without explanation as to why.“Our results suggest the importance of considering physical activity and sleep together, as these factors might combine in complex ways to influence cognitive trajectories from age 50 years onwards,” the authors concluded.Want to get more sleep?It’s a common myth in today’s stress-filled, get it all done world — we can get by on six hours of sleep or less a night. But in reality, only people with a short sleep gene have that ability.For most of us, sleeping less than six hours a night harms more than just the brain. Short sleepers have a fivefold increased risk for stroke and combined with other common conditions, such as diabetes or high blood pressure, can double the risk for heart disease and death.If you’re sleeping less than optimally out of choice, it may be time to rethink that decision. If you suffer from insomnia, sleep apnea or other sleep disorders, seeing a sleep specialist is key, experts say. In the meantime, here are some healthy sleep habits you can try.First, forget sleeping pills. They only mask the problem, experts say, and may be dangerously addictive. Instead focus on sleep hygiene, by transforming your sleep environment.In the bedroom, keep it cool — between 60 and 67 degrees Fahrenheit is best for good sleep. Don’t watch TV or work in your bedroom; you want your brain to think of the room as only for sleep.Ban all light, including the blue light of mobile phones or laptops, which signal your body to wake up.Rethink coffee in the afternoon — and that nightcap. Using alcohol to sleep will cause you to wake up within a few hours and when you sleep again, it’s typically poor quality.One of the most important things to do, experts say, is to make a sleep schedule and stick to it. Your brain needs to be trained to go to sleep at a certain hour and rise at a dedicated time every day of the week, including weekends.And the golden rule of sleep? Don’t lay in bed not sleeping. If you’re not asleep within 15 to 20 minutes of your head hitting the pillow, get up and go into another dimly lit room. Don’t turn on the television or look at your phone or laptop — instead do something mindless, like fold laundry. Once you feel sleepy, head back to bed.And don’t fret — that never put anyone to sleep. Keep training your brain, and it will respond with some well-needed z’s.